pattern2id: Match patterns against token types

In quanteda: Quantitative Analysis of Textual Data

Match patterns against token types

Description

Developer function to match regex, fixed or glob patterns against token types. This allows C++ function to perform fast searches in tokens object. C++ functions use a list of type IDs to construct a hash table, against which sub-vectors of tokens object are matched. This function constructs an index of glob patterns for faster matching.

pattern2fixed converts regex and glob patterns to fixed patterns.

index_types is an auxiliary function for pattern2id that constructs an index of "glob" or "fixed" patterns to avoid expensive sequential search. For example, a type "cars" is index by keys "cars", "car?", "c*", "ca*", "car*" and "cars*" when valuetype="glob".

Usage

pattern2id(
  pattern,
  types,
  valuetype = c("glob", "fixed", "regex"),
  case_insensitive = TRUE,
  keep_nomatch = FALSE,
  use_index = TRUE
)

pattern2fixed(
  pattern,
  types,
  valuetype = c("glob", "fixed", "regex"),
  case_insensitive = TRUE,
  keep_nomatch = FALSE,
  use_index = TRUE
)

index_types(
  pattern,
  types,
  valuetype = c("glob", "fixed", "regex"),
  case_insensitive = TRUE
)

Arguments

pattern	a character vector, list of character vectors, dictionary, or collocations object. See pattern for details.
types	token types against which patterns are matched
valuetype	the type of pattern matching: "glob" for "glob"-style wildcard expressions; "regex" for regular expressions; or "fixed" for exact matching. See valuetype for details.
case_insensitive	logical; if TRUE, ignore case when matching a pattern or dictionary values
keep_nomatch	keep patterns that did not match
use_index	construct index of types for quick search

Value

a list of integer vectors containing indices of matched types

pattern2fixed returns a list of character vectors containing types

index_types returns a list of integer vectors containing type IDs with index keys as an attribute

Examples

types <- c("A", "AA", "B", "BB", "BBB", "C", "CC")

pats_regex <- list(c("^a$", "^b"), c("c"), c("d"))
pattern2id(pats_regex, types, "regex", case_insensitive = TRUE)

pats_glob <- list(c("a*", "b*"), c("c"), c("d"))
pattern2id(pats_glob, types, "glob", case_insensitive = TRUE)

pattern <- list(c("^a$", "^b"), c("c"), c("d"))
types <- c("A", "AA", "B", "BB", "BBB", "C", "CC")
pattern2fixed(pattern, types, "regex", case_insensitive = TRUE)
index <- index_types("yy*", c("xxx", "yyyy", "ZZZ"), "glob", FALSE)
quanteda:::search_glob("yy*", attr(index, "types_search"), index)

quanteda documentation built on May 31, 2023, 8:28 p.m.